Signatures of Type III Solar Radio Bursts from Nanoflares: Modeling

TL;DR

This study models type III solar radio bursts from nanoflares to understand their properties and detectability, revealing steep frequency spectra and conditions affecting their observational signatures in closed coronal loops.

Contribution

It introduces a simple numerical model for nanoflare-induced radio emissions and applies a novel time-lag technique to analyze their signatures in closed loops.

Findings

Type III burst spectra are extremely steep, confined to narrow loop length ranges.

Detection signatures diminish with increased loop variety, burst rate, duration, or decreased brightness.

Model suggests type I bursts may originate from type III emissions in closed loops.

Abstract

There is a wide consensus that the ubiquitous presence of magnetic reconnection events and the associated impulsive heating (nanoflares) is a strong candidate for solving the solar coronal heating problem. Whether nanoflares accelerate particles to high energies like full-sized flares is unknown. We investigate this question by studying the type III radio bursts that the nanoflares may produce on closed loops. The characteristic frequency-drifts that type III bursts exhibit can be detected using a novel application of the time-lag technique developed by Viall & Klimchuk (2012) even when there are multiple overlapping bursts. We present a simple numerical model that simulates the expected radio emission from nanoflares in an active region (AR), which we use to test and calibrate the technique. We find that in the case of closed loops the frequency spectrum of type III bursts is expected to be extremely steep such that significant emission is produced at a given frequency only for a rather narrow range of loop lengths. We also find that the signature of bursts in the time-lag signal diminishes as: (1)the variety of participating loops within that range increases; (2)the occurrence rate of bursts increases; (3) the duration of bursts increases; and (4) the brightness of the bursts decreases relative to noise. In addition, our model suggests a possible origin of type I bursts as a natural consequence of type III emission in a closed-loop geometry.